If you want to convincingly add yourself to a move you need to figure out the distance the original actor was from the camera, match that, match the camera moves and blocking and lighting, learn about rotoscope and layering, learn about motion tracking and camera tracking, probably learn about keying and then start planning the shot.

If you just want to throw yourself in a scene then learn about rotoscoping or keying, put yourself on a separate layer and try and make it look good.